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Posted by Ignoramus22498 on April 23, 2008, 8:05 pm
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> Jon Danniken wrote:
>> "Don Foreman" wrote:
>>> A significant advantage to TIG is the ability to control heat
>>> independently from rate of addition of filler metal.
>>>
>>> Inability to control heat with a foot control would be a major
>>> compromise. I wouldn't consider a TIG without foot control. I have no
>>> problem with older transformer-based machines that do have foot
>>> control. That's what mine is. (Miller Dialarc 250HF)
>>
>> Thanks Don, that is what I was hoping to know.
>>
>> It also brings up a desire to know what methodology is used to externally
>> control the current output of an inductive type machine (as in with a foot
>> switch) I wouldn't imagine it's done with servo's on the shunt, maybe a PWM
>> at some stage?
>
>
> There are a couple of ways of controlling the current. The newer
> machines use PWM on the output of the transformer. The older machines
> used a thing called a MagAmp that played games with controlling the
> current coupling of the AC power by saturating the core with variable DC
> levels. Sorry I can't give a better description, it's been a long time
> since I sort of understood it.
>
Most of thise transformer welders use SCRs and control their firing
angle (timing) depending on current desired.
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Posted by Don Foreman on April 23, 2008, 9:48 pm
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On Wed, 23 Apr 2008 19:05:23 -0500, Ignoramus22498
>> Jon Danniken wrote:
>>> "Don Foreman" wrote:
>>>> A significant advantage to TIG is the ability to control heat
>>>> independently from rate of addition of filler metal.
>>>>
>>>> Inability to control heat with a foot control would be a major
>>>> compromise. I wouldn't consider a TIG without foot control. I have no
>>>> problem with older transformer-based machines that do have foot
>>>> control. That's what mine is. (Miller Dialarc 250HF)
>>>
>>> Thanks Don, that is what I was hoping to know.
>>>
>>> It also brings up a desire to know what methodology is used to externally
>>> control the current output of an inductive type machine (as in with a foot
>>> switch) I wouldn't imagine it's done with servo's on the shunt, maybe a PWM
>>> at some stage?
>>
>>
>> There are a couple of ways of controlling the current. The newer
>> machines use PWM on the output of the transformer. The older machines
>> used a thing called a MagAmp that played games with controlling the
>> current coupling of the AC power by saturating the core with variable DC
>> levels. Sorry I can't give a better description, it's been a long time
>> since I sort of understood it.
>>
>
>Most of thise transformer welders use SCRs and control their firing
>angle (timing) depending on current desired.
Some do. I think that started with the Synchrowave in the Miller
line. Older ones use saturable reactors or "mag amps" as John noted.
The DialArc uses a magamp.
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Posted by Ignoramus26128 on April 24, 2008, 10:38 am
Please log in for more thread options > On Wed, 23 Apr 2008 19:05:23 -0500, Ignoramus22498
>
>>> Jon Danniken wrote:
>>>> "Don Foreman" wrote:
>>>>> A significant advantage to TIG is the ability to control heat
>>>>> independently from rate of addition of filler metal.
>>>>>
>>>>> Inability to control heat with a foot control would be a major
>>>>> compromise. I wouldn't consider a TIG without foot control. I have no
>>>>> problem with older transformer-based machines that do have foot
>>>>> control. That's what mine is. (Miller Dialarc 250HF)
>>>>
>>>> Thanks Don, that is what I was hoping to know.
>>>>
>>>> It also brings up a desire to know what methodology is used to externally
>>>> control the current output of an inductive type machine (as in with a foot
>>>> switch) I wouldn't imagine it's done with servo's on the shunt, maybe a
PWM
>>>> at some stage?
>>>
>>>
>>> There are a couple of ways of controlling the current. The newer
>>> machines use PWM on the output of the transformer. The older machines
>>> used a thing called a MagAmp that played games with controlling the
>>> current coupling of the AC power by saturating the core with variable DC
>>> levels. Sorry I can't give a better description, it's been a long time
>>> since I sort of understood it.
>>>
>>
>>Most of thise transformer welders use SCRs and control their firing
>>angle (timing) depending on current desired.
>
> Some do. I think that started with the Synchrowave in the Miller
> line. Older ones use saturable reactors or "mag amps" as John noted.
> The DialArc uses a magamp.
Don, you are right.
--
Due to extreme spam originating from Google Groups, and their inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
more readers you will need to find a different means of
posting on Usenet.
http://improve-usenet.org/
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Posted by Jon Danniken on April 24, 2008, 10:33 am
Please log in for more thread options "Ignoramus22498" wrote:
> On 2008-04-24, BobH wrote:
>> There are a couple of ways of controlling the current. The newer
>> machines use PWM on the output of the transformer. The older machines
>> used a thing called a MagAmp that played games with controlling the
>> current coupling of the AC power by saturating the core with variable DC
>> levels. Sorry I can't give a better description, it's been a long time
>> since I sort of understood it.
>>
>
> Most of thise transformer welders use SCRs and control their firing
> angle (timing) depending on current desired.
Thanks Bob, and Iggy. I hadn't thought about the saturable reactor, but I
can see that would work (would be a bit beyond a retrofit, though). Looks
like I might have to play with an SCR to see if I can cobble something
up....
Jon
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Posted by Leon Fisk on April 24, 2008, 2:37 pm
Please log in for more thread options On Thu, 24 Apr 2008 07:33:34 -0700, "Jon Danniken"
>"Ignoramus22498" wrote:
>> On 2008-04-24, BobH wrote:
>>> There are a couple of ways of controlling the current. The newer
>>> machines use PWM on the output of the transformer. The older machines
>>> used a thing called a MagAmp that played games with controlling the
>>> current coupling of the AC power by saturating the core with variable DC
>>> levels. Sorry I can't give a better description, it's been a long time
>>> since I sort of understood it.
>>>
>>
>> Most of thise transformer welders use SCRs and control their firing
>> angle (timing) depending on current desired.
>
>Thanks Bob, and Iggy. I hadn't thought about the saturable reactor, but I
>can see that would work (would be a bit beyond a retrofit, though). Looks
>like I might have to play with an SCR to see if I can cobble something
>up....
>
>Jon
Something else to consider too is that most of the older
transformer units of any size draw a lot of current on the
input side even idling. There is a good chance you wouldn't
be able to just plug one of them in the same place as your
current buzz box without beefing up the circuit.
Make sure you check on this before getting something that
calls for a lot of re-wiring. At least figure it into the
cost of the unit.
--
Leon Fisk
Grand Rapids MI/Zone 5b
Remove no.spam for email
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